Principle: You can do a lot less work for nearly the same benefit.

Italian economist Vilfredo Pareto might be one of the least-appreciated geniuses in history. His brainchild, The Pareto Principle states that for almost all endeavors and processes, 20% of the inputs lead to 80% of the outputs. Yep, this is the old 80/20 rule.

In gym-practice, this simply means that doing one hard set provides roughly 80% of the benefit of 3-4 sets (give or take). Put another way, we're talking about the law of diminishing returns. Yes, each additional set leads to more benefit, but those benefits dwindle significantly with each new set.

If you cultivate a deep appreciation for this idea, it can come in really handy, especially when time and energy are in short supply. Just as an example, if you're short on time and high on stress, knowing that 1-2 hard sets is almost as good as 4-5 will encourage you to get in a quick workout rather than bailing out altogether.